Methods and devices for the detection of hypopnoea

ABSTRACT

Automated methods provide hypopnea detection for determining a hypopnea event and/or a severity of a hypopnea event. In some embodiments, a calculated short-term variance of a measured respiratory flow signal are compared to first and second proportions of a calculated long-term variance of the measured flow signal. A detection of the hypopnea may be indicated if the first measure falls below and does not exceed a range of the first and second proportions during a first time period. In some embodiments, a hypopnea severity measure is determined by automated measuring of an area bounded by first and second crossings of a short-term measure of ventilation and a proportion of a long-term measure. The detection methodologies may be implemented for data analysis by a specific purpose computer, a detection device that measures a respiratory airflow or a respiratory treatment apparatus that provides a respiratory treatment regime based on the detected hypopneas.

CROSS REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of the filing date of U.S.Provisional Patent Application No. 61/184,592 filed Jun. 5, 2009, thedisclosure of which is hereby incorporated herein by reference.

FIELD OF THE TECHNOLOGY

The present technology relates to methods and apparatus for detection ofhypopnea.

BACKGROUND OF THE TECHNOLOGY

Patients with OSA have recurrent apnoeas or hypopnoeas during sleep thatare only terminated by the patient arousing. A hypopnea may beconsidered a partial reduction in breathing that lasts at least 10seconds during sleep. The 1999 American Academy of Sleep Medicine (AASM)guidelines specify a hypopnea condition as a 10 second reduction in flowof 50% or more or a reduction of flow of less than 50% followed by anarousal or a desaturation of at least 3%. Subsequent AASM guidelinesspecify a 30% reduction in ventilation and a desaturation of at least 4%as a hypopnea condition. These recurrent events cause sleepfragmentation and stimulation of the sympathetic nervous system. Thiscan have severe consequences for the patient including day-timesleepiness (with the attendant possibility of motor-vehicle accidents),poor mentation, memory problems, depression and hypertension. Patientswith OSA are also likely to snore loudly, thus also disturbing theirpartner's sleep.

The best form of treatment for patients with OSA is constant positiveairway pressure (CPAP) applied by a blower (compressor) via a connectinghose and mask. The positive pressure prevents collapse of the patient'sairway during inspiration, thus preventing recurrent apnoeas orhypopnoeas and their sequelae. Such a respiratory treatment apparatuscan function to supply the patient with a supply of clean breathable gas(usually air, with or without supplemental oxygen) at the therapeuticpressure or pressures, at appropriate times during the subject'sbreathing cycle.

Respiratory treatment apparatus typically include a flow generator, anair filter, a mask or cannula, an air delivery conduit connecting theflow generator to the mask, various sensors and a microprocessor-basedcontroller. The flow generator may include a servo-controlled motor andan impeller. The flow generator may also include a valve capable ofdischarging air to atmosphere as a means for altering the pressuredelivered to the patient as an alternative to motor speed control. Thesensors measure, amongst other things, motor speed, gas volumetric flowrate and outlet pressure, such as with a pressure transducer, flowsensor or the like. The apparatus may optionally include a humidifierand/or heater elements in the path of the air delivery circuit. Thecontroller may include data storage capacity with or without integrateddata retrieval/transfer and display functions.

To treat hypopnea, automated apparatus have been implemented withalgorithms to detect a hypopnea condition based on data from a flowsensor. Examples of conventional apnea/hypopnea detection devices aretaught in U.S. Pat. No. 5,295,490 to Dodakian; U.S. Pat. No. 5,605,151to Lynn; U.S. Pat. No. 5,797,852 to Karakasoglu et al.; U.S. Pat. No.5,961,447 to Raviv et al.; U.S. Pat. No. 6,142,950 to Allen et al.; U.S.Pat. No. 6,165,133 to Rapoport et al.; U.S. Pat. No. 6,368,287 to Hadas;U.S. Pat. No. 7,118,536 to Haberland et al. For example, in one suchdevice, a hypopnoea can be deemed detected if a 10 or 12 second rootmean square (RMS) of a flow (in L/sec) signal drops below 1.2 times thelong-term average minute ventilation (in L/sec) (e.g., low passfiltering the absolute value of a flow signal divided in half), whichapproximately corresponds to a reduction to 50% of the normal RMSventilation. A 50% reduction of an RMS ventilation may also be detectedby comparing a ten second variance of a flow signal calculated over a 10second window with the product of (0.5)² and a sixty second variance ofa flow signal calculated over a 60 second window. Such devices may alsoinclude a refractory period of time after detecting a hypopnea toprevent multiple scoring of a common hypopnea event. For example, thedevice may remain refractory for 15 seconds or until the RMS ventilationreturns to at least three quarters of a long-term RMS ventilation for 15contiguous seconds.

However, the question of the presence of a hypopnea condition itself issubject to interpretation. There is often considerable clinicianvariability in scoring the presence of a hypopnea. Thus, while automatedapparatus may be implemented with various methods to detect thecondition, differences in the implemented detection criteria can resultin different hypopnea scoring for common breathing events.

It may be desirable to develop further methods for detecting hypopneawhich may also be implemented in apparatus for detection and apparatusfor treating upper respiratory conditions.

SUMMARY OF THE TECHNOLOGY

A first aspect of some embodiments of the present technology is toprovide methods and devices for detecting a hypoponea and/or a severityof a hypopnea.

Another aspect of some embodiments of the technology is to detecthypopneas or hypopnea severity in an apparatus that measures arespiratory flow signal of a patient.

A still further aspect of the technology is to implement the detectionof hypopnea or hypopnea severity in a respiratory treatment apparatus,such as a continuous positive airway pressure device, based on or as afunction of the detected hypopneas or hypopnea severity.

Some embodiments of the present technology involve an apparatus orcontroller with a method for controlling a processor to detect ahypopnea from a measured flow of breathable gas. The method of thecontroller or processor may involve determining a first measure from ashort-term variance of data based on a measured flow of breathable gas.It may further involve determining a second measure from a long-termvariance of data based on a measured flow of breathable gas. The firstmeasure may be compared with first and second proportions of the secondmeasure. With the method, the apparatus or controller may indicate adetection of the hypopnea based on the comparing if the first measurefalls below the first proportion and does not subsequently exceed arange of the first and second proportions during a first time period.

In some embodiments, the first proportion may be less than the secondproportion and the method may also involve indicating a detection of ahypopnea if the first measure does not exceed the first proportionduring the first time period. Moreover, the method may also involveindicating a detection of a hypopnea if the first measure exceeds thefirst proportion but does not exceed the second proportion during thefirst time period. In some embodiments, the comparing of the firstmeasure and the first proportion represents a determination of whetheran RMS value calculated from approximately ten to twenty seconds, butpreferably twelve seconds, of respiratory flow data falls below athreshold of approximately fifty percent of an RMS value calculated fromapproximately fifty to seventy seconds, but preferably sixty seconds, ofrespiratory flow data and wherein the first period of time isapproximately three to eight seconds, but preferably four seconds.Moreover, the comparing of the second measure and the second proportionmay represent a determination of whether an RMS value calculated fromapproximately ten to fifteen seconds, but preferably twelve seconds, ofrespiratory flow data is below a threshold of approximately seventy fivepercent of an RMS value calculated from approximately fifty to seventyseconds, but preferably sixty seconds, of respiratory flow data.

Optionally, further detections of a hypopnea may be impeded until thefirst measure exceeds the second proportion during a second period oftime. This impeding of a further detection may involve comparing of thefirst measure and the second proportion such that the comparingrepresents a determination of whether an RMS value calculated fromapproximately ten to fifteen seconds, but preferably twelve seconds, ofrespiratory flow data exceeds a threshold of approximately seventy fivepercent of an RMS value calculated from approximately fifty to seventyseconds, but preferably sixty seconds, of respiratory flow data andwherein the second period of time is approximately ten to twenty secondsbut preferably fifteen, seconds. In some cases, the time from which thelong term measure of ventilation is calculated may be at leastapproximately three to five times that of the time from which the shortterm measure is calculated.

Some embodiments of the present technology involve an apparatus orcontroller with a method for controlling a processor to detect ahypopnea from a measured flow of breathable gas. The method of theprocessor or controller may include determining a long-term measure ofventilation and a short-term measure of ventilation. The method of theprocessor or controller may further include determining a threshold as aproportion of the long-term measure of ventilation and measuring an areabounded by first and second crossings of the short-term measure ofventilation and the threshold. A hypopnea is then detected with themeasured area. The measuring may involve integrating a differencebetween the threshold and the short-term measure of ventilation during atime period from when the short-term measure falls below the thresholdto when the short-term measure exceeds the threshold. In someembodiments, the measuring comprises adding a plurality of sampledifferences during a time period from when the short-term measure fallsbelow the threshold to when the short-term measure exceeds thethreshold. Each sample difference may be a difference between a sampleof the threshold and a sample of the short-term measure of ventilation.

Optionally, the method of the apparatus or controller may be configuredto impede a further detection of a hypopnea during a refractory periodinitiated at the second crossing. Moreover, the method may includetriggering the measuring of the area upon detecting the first crossingby comparing the short-term measure of ventilation and the threshold forinequality. Still further, the detecting of the hypopnea may becontingent upon a time from the first crossing to the second crossingexceeding about ten seconds. In some embodiments, the short-term measureof ventilation may be an output of low pass filtering half of anabsolute value of a measure of flow of breathable gas with a first timeconstant. Similarly, the long-term measure of ventilation may be anoutput of low pass filtering half of an absolute value of a measure offlow of breathable gas with a second time constant larger than the firsttime constant. Optionally, the proportion may be set at approximatelyseventy percent. In some embodiments, the device or apparatus mayindicate a severity of the hypopnea with the measure of area.Optionally, the device or apparatus may compare the measured area with athreshold chosen to be approximately indicative of a desaturation ofblood oxygen of at least four percent.

Some embodiments of the present technology involve an apparatus orcontroller with a method for controlling a processor to detect ahypopnea from a measured flow of breathable gas that includes thecontroller or a processor determining a long-term measure of ventilationand a short-term measure of ventilation. A threshold is then determinedas a proportion of the long-term measure of ventilation. The controlleror processor then calculates an extent of a hypopnea as a function ofthe short-term measure of ventilation and the threshold. The apparatusthen indicates a severity of the hypopnea with the measured extent,which may involve outputting a value of the measured extent. Thecalculated extent may be a calculated area bounded by first and secondcrossings of the short-term measure of ventilation and the threshold.The calculated area may then optionally be compared with a thresholdchosen to be approximately indicative of a desaturation of blood oxygenof at least four percent.

In some embodiments, the method of the apparatus or controller mayfurther detect a measure of flow limitation from a measured flow ofbreathable gas and wherein the indicating the detection of the hypopneais further based on the measure of flow limitation being indicative ofobstruction.

Still further embodiments of the technology may involve a methodologyfor controlling a processor to classify a hypopnea from a measured flowof breathable gas. The method of the processor may include detecting anhypopnea event from a measured flow of breathable gas. It may furtherinclude determining a measure indicative of obstruction in the measuredflow coincident with the hypopnea event. The method may also includeclassifying the detected hypopnea event as obstructive or central basedon the determining of the measure indicative of obstruction. In somesuch embodiments, the determining comprises detecting partialobstruction and the classifying comprises scoring an obstructivehypopnea event. In some such embodiments, the method may also involvedetecting an absence of a breath and the classifying may involve scoringa central hypopnea event based on the absence of a breath. In analternative embodiment, the method may also involve detecting an absenceof a breath coincident with a detected hypopnea event and refrainingfrom scoring the detected hypopnea event as either central hypopnea orobstructive hypopnea based on the absence of the breath. In such a case,the event may be considered to be an apnea.

In some embodiments, the technology may be implemented as a hypopneadetection apparatus. In such an apparatus, an included controller mayhave at least one processor to access data representing a measured flowof breathable gas. The controller may be configured to control adetection of an hypopnea event from the data representing the measuredflow of breathable gas. It may also be configured to control adetermination of a measure indicative of obstruction coincident with thehypopnea event in the data representing the measured flow. It may alsobe configured to control a classification of the detected hypopnea eventas obstructive or central based on the determining of the measureindicative of obstruction. In some such embodiments, the classificationdetects partial obstruction and the classification comprises scoring anobstructive hypopnea event. In some such embodiments, the controller maybe further configured to control a detection of an absence of a breathand the classification may involve scoring a central hypopnea event. Inan alternative embodiment, the controller may determine an absence of abreath coincident with a detected hypopnea event and refrain fromscoring the event as either central hypopnea or obstructive hypopneabased on the detected absence of the breath. In such a case, the eventmay be considered to be an apnea. Such an apparatus may also include aflow generator configured to produce a breathable gas for a patient at apressure above atmospheric pressure and a flow sensor. The controllermay then be configured to measure the flow of breathable gas with theflow sensor and to control the flow generator to produce the breathablegas according to a pressure therapy regime based on the detectedhypopnea.

Additional features of the present respiratory technology will beapparent from a review of the following detailed discussion, drawingsand claims.

BRIEF DESCRIPTION OF DRAWINGS

The present technology is illustrated by way of example, and not by wayof limitation, in the figures of the accompanying drawings, in whichlike reference numerals refer to similar elements including:

FIG. 1 shows an example hypopnea detection apparatus of the presenttechnology with an optional flow sensor and flow generator;

FIG. 2 is a flow diagram of an example embodiment of a method ofcontrolling an apparatus to detect a hypopnea;

FIG. 3 is a state diagram of a further example apparatus that mayimplement a method of detecting a hypopnea;

FIG. 4 is a graph illustrating a detection correlation of an exampleembodiment of the methodologies of the present technology;

FIG. 5 is a further flow diagram of another example embodiment of amethod of controlling an apparatus to detect a hypopnea and/or hypopneaseverity;

FIG. 6 is an illustration of a graph of a measure for detecting hypopneaand/or measuring an hypopnea severity; and

FIG. 7 is a block diagram of a controller in a hypopnea detectionapparatus including example components thereof suitable for implementingthe detection methodologies of the present technology.

DETAILED DESCRIPTION

As illustrated in FIG. 1, embodiments of the present technology mayinclude a hypopnea detection device or apparatus having a controller 104that may have one or more processors to implement particular hypopneadetection methodologies such as the algorithms described in more detailherein. Thus, the device or apparatus may include integrated chips, amemory and/or other control instruction, data or information storagemedium. For example, programmed instructions encompassing such detectionmethodologies may be coded on integrated chips in the memory of thedevice or apparatus to form an application specific integrated chip(ASIC). Such instructions may also or alternatively be loaded assoftware or firmware using an appropriate data storage medium. With sucha controller or processor, the device can be used for processing datafrom a flow signal. Thus, the processor may control the assessment of ahypopnea occurrence or severity as described in the embodimentsdiscussed in more detail herein based on measured and recordedrespiratory flow data from a prior sleep session. Alternatively, thedetection may be performed during a sleep session contemporaneously withthe measuring of a respiratory flow signal. Thus, in some embodiments,the device or apparatus itself may optionally be implemented with a flowsensor 106 for measuring a respiratory flow signal for use with theimplemented methodologies. For example, flow to or through a nasalcannula 108 or mask may be measured using a pneumotachograph anddifferential pressure transducer or similar device such as one employinga bundle of tubes or ducts to derive a flow signal. Optionally, a flowsignal may be inferred from other sensors, such as, a motor currentsensor as described in PCT/AU2005/001688 filed on Nov. 2, 2005, and U.S.patent application Ser. No. 12/294,957, the National Stage thereof, theentire disclosures of which is incorporated herein by cross reference.

By way of further example, the hypopnea detection device may beimplemented with a control methodology to respond to detected hypopneaas a respiratory treatment apparatus. For example, as illustrated inFIG. 1, detection device may be optionally implemented with a flowgenerator such as a servo controlled blower with suitable sensors forsuch control (e.g., a pressure sensor). A respiratory treatment orpressure therapy regime, such as a therapeutic pressure level associatedwith CPAP treatment, may be delivered by the controller of the device.Such therapeutic pressure levels may be automatically adjusted inresponse to the detection of hypopnea conditions as described herein.For example, pressure levels may be increased by a specified amount upondetection of a hypopnea. Optionally, it may be increased proportionallyas a function of a detected hypopnea severity. For example, a hypopneawith a greater severity measure may yield a greater pressure adjustmentthen a hypopnea with a lesser severity measure. Other pressureadjustment schemes may also be implemented.

In some embodiments, the hypopnea detector may implement a detection ofa hypopnea according to AASM guidelines. For example, the detector maybe constructed to score a hypopnea event upon detection of a reductionin ventilation by about 30% or more for about 10 seconds or more coupledwith the detection of a desaturation of blood oxygen by about 4% ormore. In such an embodiment, the reduction in ventilation may, forexample, be determined by a measure of ventilation such as a tidalvolume or other such measure based on the measured respiratory flowsignal. Optionally, the measure of ventilation may be derived byprocessing of determined breath peak inspiratory and/or breath peakexpiratory flows. Similarly, the reduction of blood oxygen may be basedon data from an oximetry signal from an optional oximetry sensor (notshown in FIG. 1). However, as discussed in more detail herein, otherembodiments of the present technology may be implemented to emulate suchan AASM guideline without analysis of oximetry data from an oximetrysensor.

(1) Example Detection Features

As illustrated in the flow chart of FIG. 2, in some embodiments of thepresent technology an automated detection of a hypopnea condition by adetection device may be based on the determination or calculation of avariance from data representing a measure of a flow of breathable gas ora respiratory flow signal. For example, at 220 a first measure from ashort-term variance calculation may be determined. One such measure maybe calculated by determining the mean of the squares minus the square ofthe mean of the samples from a respiratory flow signal from a flowsensor or recorded data based thereon. Other methods for calculating thevariance may also be implemented. The short-term variance may be on theorder of seconds, such as about ten to fifteen seconds, for example a 10second variance utilizing about ten seconds of samples taken from theflow signal. Similarly, a long-term variance measure may be determinedat 222. The long-term variance may be on the order of minutes such asapproximately one minute or about fifty to seventy seconds, for example,60 seconds utilizing about sixty seconds of samples taken from the flowsignal. In some cases, the time from which the long term measure ofventilation is calculated may be at least approximately three to fivetimes that of the time from which the short term measure is calculated.For example, is the long term measure of ventilation is chosen to becalculated from sixty seconds, the short term measure may be calculatedas one fifth (e.g., 60/5) to give a time period of twelve seconds.

At 224, a measure of the short-term variance may be compared with firstand second proportions of the long-term variance. For example, it may bedesired to detect a hypopnea based on a decrease that does not exceed acertain range, for example, between of 45% and 70%. In such a case, thelong-term variance may be multiplied by factors of (0.45)² and (0.7)².Optionally, these factors may be utilized without the squaringoperations if they are multiplied by the square root of the long-termvariance and the resulting proportions are compared with the square rootof the short-term measure of variance. Such a comparison represents adetermination of a reduction in airflow based on RMS ventilation. At226, a hypopnea event may then be scored or indicated when the measureof the short-term variance falls below the first proportion but does notsubsequently exceed a range of the first and the second proportions fora period of time. Such a system may permit more accurate automateddetection or scoring of hypopnea, by permitting brief excursions of dataof the respiratory flow signal above the first proportion but not thesecond while a time period of the fall in patient breathing isaccumulated or timed.

A state diagram for implementing such an embodiment of the technology ina detector is illustrated in FIG. 3. The detector may be useful for adevice that contemporaneously scores hypopnea during a sleep sessionwith the detector while a patient is experiencing the event but it mayalso be implemented for post-session analysis. The behavior of thedevice begins at a start state S0. At 332, the device may determinewhether the RMS ventilation falls below about a 50% threshold. Forexample, the device may compare a short-term variance of a respiratoryflow signal determined over a 10 or 12 second data window (i.e., V₁₀ orV₁₂) with a proportion of a long-term variance determined over a sixtysecond data window (e.g., (0.5)² times V₆₀). If this threshold is met orbreached, a timing period may be triggered or started at 334 and thedevice enters a sub-50 state (S1). For example, a count down timer(designated “Sub-50 Timer”) may be set to a maximum period of aboutthree to eight seconds, but preferably four seconds. Other values forthis time setting may be pre-determined depending on the desired resultsof hypopnea evaluation criteria. If the threshold is not met at 332, thedevice returns to the start state (S0).

At 336, the device then determines whether the RMS ventilation remainsbelow about 50%. Such a test may be comparable to the test implementedat 332. If not, then the device transitions to an excursion range state(S2). From this state, the device tests whether the RMS ventilationagain falls below about 50% at 338. If it does, the device then returnsto the sub-50 state (S1). If not, then the device tests whether the RMSventilation exceeds about a 75% threshold at 340. For example, thedevice may compare the short-term variance of a respiratory flow signaldetermined over a 10 or 12 second data window (i.e., V₁₀ or V₁₂) withanother proportion of the long-term variance determined over a sixtysecond data window (e.g., (0.75)² times V₆₀). If this threshold is metor breached, then the device may transition to the start state (S01)without scoring a hypopnea event. If at 340 the threshold is not met,then the device returns to the excursion range state (S2).

If at 336 the test determines that the RMS ventilation remains belowabout 50%, then the Sub-50 Timer is decremented or permitted to countdown if it has not expired (e.g., if it greater than 0) at process block342. Then, at 344, the Sub-50 Timer is checked for an expirationcondition such that the timing period has expired or lapsed. If it hasnot expired the device remains in the sub-50 state (S1). If it hasexpired, the device scores a hypopnea upon entering the scored state(S3). Thus, detection device indicates a hypopnea condition based on theanalysis of the sub-50 state (S1) and the excursion range state (S2).

Another feature of the device once having entered the scored state (S3)is the implementation of a refractory period to prevent multiple scoringof a common hypopnea event. Thus, at 346 the RMS ventilation is testedto see if it exceeds about a 75% threshold. The test is comparable tothe comparison at 340. If at 346 it does not exceed the threshold, thedevice remains in the scored state (S3). If at 346 it does exceed thethreshold, another timing period or a refractory timing period may betriggered or started at 348 and the device enters a super-75 state (S4).For example, a count down timer (designated “Super-75 Timer”) may be setto a maximum period of about ten to twenty seconds, but preferably 15seconds. Other values for this time setting may be pre-determineddepending on the desired length of the refractory time to ensure thatthe scored hypopnea condition has ceased.

From the super-75 state (S4), the RMS ventilation is checked at 350 forconfirmation that it remains above the threshold of about 75% like thecomparison at 346. If it does, then at 352 the Super-75 Timer isdecremented so it continues to run or count down. If at 354, theSuper-75 Timer has expired or passed the desired time period, then thedevice returns to the start state (S0). If not, the device remains inthe super-75 state (S4).

In sum, the detector determines whether the short-term ventilationmeasure falls below a 50% threshold and then stays there for about 4seconds. The detector allows excursions above the 50% threshold but nota 75% threshold while the 4 second period is being accumulated. However,if the 75% threshold is exceeded before the accumulation period is overthen the detector will reset to start without a hypopnea indication.Once the accumulation is complete, a hypopnoea is indicated. Thedetector then requires the short-term threshold measure to exceed a 75%threshold for a refractory period such as 15 contiguous seconds beforethe detector becomes non-refractory. As implemented, the detector willnot score short hypopnoeas and will tend to allow messy periods ofdepressed flow to be scored as one hypopnoea rather than two or more.

In some embodiments, entering the stored state (S3) or otherwiseindicating or scoring a hypopnea may be further conditioned on adetection of flow limitation, an obstructive apnea and/or central apnea,which may be detected by a common processor as the hypopnea detectionprocessor or a different processor in electronic communication with thehypopnea detection processor. For example, the device may be configuredto also detect an obstructive apnea, partial obstruction and/or centralapnea by any of the methods described in U.S. Pat. Nos. 6,138,675 and6,029,665, the entire disclosures of which are incorporated herein bycross reference, which a different processor or detector. Similarly, thedevice may be configured to detect a measure of flow limitation, such asa fuzzy flow limitation measure as disclosed in PCT/AU008/000647, filedon May 9, 2008, (published as International Patent ApplicationPublication No. (WO/2008/138040) and U.S. Provisional Patent ApplicationNo. 60/965,172 filed on Aug. 17, 2007, the disclosures of which arehereby incorporated herein by reference. In such embodiments, thedetermination of the reduction in ventilation (e.g., a classificationassociated with the sub-50 state) in conjunction with a detection of anyone or more of a central apnea, patency of the airway, an absence ofpartial obstruction, an obstructive apnea or a low or insufficientmeasure of flow limitation, may be taken as a contra-indication ofhypopnea condition. In such a case, the decrease in ventilation may beconsidered a result of apnea. For example, if a measure of partialobstruction or flow limitation indicates that there is insignificant orno obstruction during the sub-50 timing period, then rather than scoringa hypopnea, the detector may return to the start state (S0) or a furtherwait state (not shown) that provides a similar refractory timing periodto wait for the ventilation measure to return above a threshold such asthe 75% threshold discussed at 346. Similarly, by way of furtherexample, if a measure of central apnea or airway patency indicates thatthere is a central apnea during the sub-50 timing period, then ratherthan scoring a hypopnea, the detector may return to the start state (S0)or the further wait state that provides a similar refractory timingperiod to wait for the ventilation measure to return above a thresholdsuch as the 75% threshold discussed at 346. As a still further example,if a measure of obstructive apnea indicates that there is an obstructiveapnea during the sub-50 timing period, then rather than scoring ahypopnea, the detector may return to the start state (S0) or the furtherwait state that provides a similar refractory timing period to wait forthe ventilation measure to return above a threshold such as the 75%threshold discussed at 346.

An embodiment of the above detector based on the state diagram of FIG. 3was tested on a library of data representing recorded patientrespiratory flow signals. The flow data was pre-correlated with oxygendesaturation data. The hypopnea detector analyzed the flow data andhypopnea events were recorded. The hypopnea events detected were thencorrelated with the desaturation event data. A graph of the correlationis illustrated at FIG. 4. The graph shows that the hypopnea detectionmethodology correlates well with desaturation events (ODI) of at least a4% desaturation.

In a further example of the scoring methodology illustrated in FIG. 3,the states of the state machine may be implemented to avoid scoring thehypopnea when apnea events (e.g., central apnea or obstructive apnea)are detected. For example, when the detector enters the scored state(S3), an hypopnea is merely “pre-logged” (such as by setting a“pre-logged” variable to true) so that it is not scored immediately.This may be considered the detection of a potential hypopnea by thedetector. At this time, an apnea detector (such as an obstructive apneaand/or central apnea detector) may be polled (e.g., continuously duringthe state) to determine if the apnea detector has detected an apnea. If,in response to the polling, the detection of apnea has been confirmed,then the value of the “pre-logged” variable may be changed (e.g., set tofalse) and the state of the hypopnea detector is advanced to thesuper-75 state (S4) with the setting of the Super75 Timer at 348. Inthis way, the scoring of the hypopnea may be bypassed. Once the detectoradvances to the super-75 state (S4) then a potential hypopnea event willbe logged or scored as an hypopnea event based on the pre-loggedvariable (e.g., if “pre-logged” variable is true, the event is logged asan hypopnea; but if the “pre-logged” variable is false, the event willnot be logged or scored as a hypopnea.)

In this embodiment, the state machine of the detector advances out ofthe scored state (S3) by entering the super75 state (S4). Therefore, ifat any time between entering the scored state and entering the super75state (S4) an apnea is confirmed, then no hypopnea will be logged.Further, if at any time an apnea is confirmed before an hypopnea isscored, then the hypopnea detector is put into the refractory state andno score is possible until the refractory period is over. Thus, thisembodiment can help to prevent false positive hypopnea scoring when apotential hypopnea event is an apnea event. While this embodimentimplements a coordinated apnea and hypopnea detection by separatedetectors (e.g., separate devices or separate software and/or hardwaremodules of a common apparatus) that communicate through polling asdescribed above, in some embodiments, the states of the state machineabove may be modified with additional thresholds intended for detectingapnea by known methods. In such a case, the output of a unified statemachine of a common software and/or hardware module could be to detecteither a hypopnea condition or an apnea condition depending on theresults of the assessments of the various thresholds or conditions ofthe state machine.

(2) Additional Detection Features

In some embodiments, a scoring of a hypopnea may also include adetermination of a measure of the severity of the scored hypopnea. Anexample of such a methodology is illustrated in FIG. 5. In the example,short-term and long-term measures of ventilation may be determined froma respiratory flow signal respectively at 540 and 542. For example, themeasures may be an RMS ventilation or variance calculation as discussedin the prior embodiment determined over short and long time windows(e.g., about 12 and 60 seconds respectively). By way of further example,the ventilation measures may each be a low pass filtered averageventilation (e.g., half of the absolute value of data samples from aflow signal using short and long time constants). In still furtherembodiments, a long-term average tidal volume over multiple breaths anda recent tidal volume of one or an average of several breaths may beutilized as ventilation measures. At 544 a threshold as a function ofthe long-term measure is determined. For example, the threshold may be aportion or proportion of the measure (e.g., 50%, 75%, etc.). Thethreshold may be empirically determined based on hypopnea conditions inpatients. Then at 546, the detection device detects a hypopnea or theseverity of a hypopnea with the threshold and the short-term measure by,for example, measuring an area bounded by first and second crossings ofthe short-term measure of ventilation and the threshold.

An example of the technology may be considered in conjunction with theillustrated graph of FIG. 6. The graph plots a long-term ventilationmeasure 650 and a short-term ventilation measure 652, which may bedetermined from a measured respiratory flow signal. The graph alsoillustrates a threshold 650P determined as a function of the long-termventilation measure. The extent of the bounded area A, which may providea measure of severity of a hypopnea incident, may be determined by thedetection device with the data from these measures. For example, thisbounded area A may be determined by the following example formula:A=∫ _(a) ^(b) f(x)−g(x)dxWhere:

f(x) is a proportion of a long-term measure of ventilation;

G(x) is the short-term measure of ventilation;

a and b are first and second crossings of f(x) and g(x), and may delimita period of time at least ten seconds in length.

In an example embodiment, the integration of the ventilation measuresmay be implemented by sampling of these signals at a common time and byconsecutively adding sample differences of the threshold and theshort-term measure (i.e., f(x)−g(x), where x is a sample time) from time(a) to time (b). As shown in FIG. 6, the adding operation may beinitiated (at “Trigger a”) by comparing the threshold and the short-termmeasure to determine that the short-term measure is less than thethreshold (e.g., G(x)<=F(x) at x=a). The adding operation may then stop(at “Trigger b”) by again comparing the threshold and short-termventilation (e.g., G(x)>=F(x) at x=b) to determine that the short-termmeasure has exceeded the threshold. The resulting sum may be taken asthe severity measure. In some embodiments, if the time period over whichsamples were taken (e.g., a sample count) does not exceed a chosen timeperiod indicative of hypopnea, such as about 10 seconds, the measure ofseverity may be disregarded (e.g., if (b−a)<10 seconds).

These area determination methods of FIG. 5 may optionally be implementedalong with the scoring methodologies of FIGS. 2 and 3 to provide aseverity measure for each scored event and/or to provide a jointhypoponea score based on both methodologies. For example, a hypopnea maybe counted by a detector if either method or, alternatively, bothmethods detect the occurrence of a hypopnea. The severity measure maythen be provided for the counted hypopnea. However, the area methods mayalso be implemented independent of the former methods as independentdetectors.

Thus, the area measurement may be utilized to not only score a hypopneabut to provide a measure of its severity as well. For example, theseverity measure may be compared to a threshold indicative of hypopnea.For example, a predetermined threshold may be empirically determined tobe indicative of desaturation, such as about a 4% desaturation event.Thus, by comparing the severity measure to such a threshold, a hypopneaevent may be scored. Optionally, its severity may be further analyzed orquantified by, for example, determining a value that it exceeds thethreshold or as a ratio with the threshold. Still further, the value ofthe area itself may serve as the measure of severity.

In some embodiments, the length of the hypopnea, such as its time orduration, may also serve as a measure of severity. As with the areameasure, it may be compared to one or more thresholds to assess thehypopnea event. In some embodiments, the area measure, the length orduration and the count, may be each analyzed to score a hypopnea and/ordefine its severity. For example, a hypopnea event scored by any of thedescribed embodiments may be further characterized by its length andarea to indicate severity.

In still further embodiments of the hypopnea detection technology,hypopnea events may be characterized or classified by type, such as bydetermining that an hypopnea event is an obstructive hypopnea ordetermining that the hypopnea event is a central hypopnea. In this way,the detector may distinguish between different types of hypopneas. Forexample, the common occurrence of (1) an hypopnea event detected by anyof the methodologies herein, such as in the absence of a confirmation ofa detected apnea, and (2) the detection of any one or more of (a) ameasure of flow limitation (e.g., by analysis of a flow limitationindex), (b) detecting a breath or breathing cycle during the hypopnea(e.g., confirming patient triggering of the transition from anexpiration state to inspiration state based on triggering threshold)and/or (c) a measure of partial obstruction, may be collectively takenas a detection of an obstructive hypopnea for scoring rather than acentral hypopnea. Similarly, the common occurrence of (1) a hypopneaevent detected by any of the methodologies herein, such as in theabsence of a confirmation of a detected apnea, and (2) the detection ofany one or more of (a) a patency condition of the airway, (b) a failureto detect a breath or breathing cycle (e.g., an absence of patienttriggering of the transition from an expiration state to inspirationstate after a period of time based on triggering threshold) and/or (c)an absence of flow limitation or partial obstruction, may becollectively taken as a detection of an central hypopnea for scoringrather than an obstructive hypopnea. Thus, while a number of scoredhypopnea events may be presented as a total of both obstructivehypopneas and central hypopneas, some embodiments of the presenttechnology may also be implemented to score or report a break down ofthe number of obstructive hypopneas separately from the number ofcentral hypopneas determined by the detector.

By way of further example, in one such embodiment of the detector,obstructive hypopnea events may be scored while hypopnea events that areattributable to central events are not scored. In the example, hypopneaevents detected by any of the methods described herein that alsocoincide with a flow limitation index satisfying a desired threshold maybe scored as a hypopnea or as an obstructive hypopnea. However, in theevent that a detected hypopnea event coincides with the absence of adetection of a breath or breathing cycle, no hypopnea may be scored. Insuch a case the failure to detect a breath or breathing cycle (e.g., anabsence of patient triggering of the transition from an expiration stateto inspiration state after a period of time based on triggeringthreshold) may be considered an indicator of a central event (e.g.,central apnea).

Example Architecture

An example system architecture of a controller is illustrated in theblock diagram of FIG. 7. In the illustration, the hypopnea detectiondevice 701 or general purpose computer may include one or moreprocessors 708. The device may also include a display interface 710 tooutput hypopnea detection reports (e.g., hypopnea counts and/or severitymeasures), results or graphs (e.g., area curves as illustrated in FIG.6) as described herein such as on a monitor or LCD panel. A usercontrol/input interface 712, for example, for a keyboard, touch panel,control buttons, mouse etc. may also be provided to activate themethodologies described herein. The device may also include a sensor ordata interface 714, such as a bus, for receiving/transmitting data suchas programming instructions, oximetery data, flow data, hypopneadetection data etc. The device may also typically include a memory/datastorage components containing control instructions of the aforementionedmethodologies (e.g., FIGS. 2-6). These may include processor controlinstructions for flow or oximetery signal processing (e.g.,pre-processing methods, filters) at 722 as discussed in more detailherein. They may also include processor control instructions forventilation measure determination (e.g., variance, RMS calculationsetc.) at 724. They may also include processor control instructions forHypopnea detection or severity measurement (e.g., thresholddetermination, comparison, area measuring, triggering, timing methods,scoring etc.) at 726. Finally, they may also include stored data 728 forthese methodologies such as detected hypopnea events and/or hypopneaseverity measures, threshold proportions, timing thresholds, reports andgraphs, etc.)

In some embodiments, the processor control instructions and data forcontrolling the above described methodologies may be contained in acomputer readable recording medium as software for use by a generalpurpose computer so that the general purpose computer may serve as aspecific purpose computer according to any of the methodologiesdiscussed herein upon loading the software into the general purposecomputer.

In the foregoing description and in the accompanying drawings, specificterminology, equations and drawing symbols are set forth to provide athorough understanding of the present technology. In some instances, theterminology and symbols may imply specific details that are not requiredto practice the technology. For example, although the terms “first” and“second” have been used herein, unless otherwise specified, the languageis not intended to provide any specified order but merely to assist inexplaining distinct elements of the technology. Furthermore, althoughprocess steps in the detection methodologies have been illustrated inthe figures in an order, such an ordering is not required. Those skilledin the art will recognize that such ordering may be modified and/oraspects thereof may be conducted in parallel.

Moreover, although the technology herein has been described withreference to particular embodiments, it is to be understood that theseembodiments are merely illustrative of the principles and applicationsof the technology. It is therefore to be understood that numerousmodifications may be made to the illustrative embodiments and that otherarrangements may be devised without departing from the spirit and scopeof the technology. For example, while the above scoring and severitymeasuring methodologies may be performed without measured blood oxygendata, in some embodiments, a detector may further include access todesaturation data from an oximetry sensor to classify hypopneas withactual SpO₂ data and ventilation or airflow data, such as by a method ofthe AASM guidelines. In such an embodiment, the detector may implementhypopnea detection with the SpO₂ data and without as described in priorembodiments (e.g., FIGS. 2, 3 and 5). Thus, the device may score ahypopnea by detection with either methodology or alternatively, with adetection by both methodologies. Such an embodiment may also be utilizedto compare results from both methodologies to evaluate eithermethodology or to provide a treatment of the detected hypopneas ifdetected by either or both methodologies.

Additional example embodiments of the herein disclosed technology mayalso be understood upon consideration of the following descriptiveparagraphs. To this end, the technology may also involve:

A method for controlling a processor to detect a hypopnea from ameasured flow of breathable gas, the method of the processor comprising:determining a first measure from a short-term variance of data based ona measured flow of breathable gas; determining a second measure from along-term variance of data based on a measured flow of breathable gas;comparing the first measure with first and second proportions of thesecond measure; and indicating a detection of the hypopnea based on thecomparing if the first measure falls below the first proportion and doesnot subsequently exceed a range of the first and second proportionsduring a first time period.

The method of any of the proceeding paragraphs wherein the firstproportion is less than the second proportion and further comprisingindicating a detection of a hypopnea if the first measure does notexceed the first proportion during the first time period.

The method of any of the proceeding paragraphs wherein the firstproportion is less than the second proportion and further comprisingindicating a detection of a hypopnea if the first measure exceeds thefirst proportion but does not exceed the second proportion during thefirst time period.

The method of any of the proceeding paragraphs further comprisingdetecting a measure of flow limitation from a measured flow ofbreathable gas and wherein the indicating the detection of the hypopneais further based on the measure of flow limitation being indicative ofobstruction.

The method of any of the proceeding paragraphs wherein the comparing ofthe first measure and the first proportion represents a determination ofwhether an RMS value calculated from approximately ten to fifteenseconds of respiratory flow data falls below a threshold ofapproximately fifty percent of an RMS value calculated fromapproximately fifty to seventy seconds of respiratory flow data andwherein the first period of time is approximately three to eightseconds.

The method of any of the proceeding paragraphs wherein the comparing ofthe second measure and the second proportion represents a determinationof whether an RMS value calculated from approximately ten to fifteenseconds of respiratory flow data is below a threshold of approximatelyseventy five percent of an RMS value calculated from approximately fiftyto seventy seconds of respiratory flow data.

The method of any of the proceeding paragraphs wherein the comparing ofthe first measure and the first proportion represents a determination ofwhether an RMS value calculated from approximately ten to fifteenseconds of respiratory flow data falls below a threshold ofapproximately fifty percent of an RMS value calculated fromapproximately fifty to seventy seconds of respiratory flow data andwherein the first period of time is approximately three to eightseconds.

The method of any of the proceeding paragraphs further comprisingimpeding a further detection of a hypopnea until the first measureexceeds the second proportion during a second period of time.

The method of any of the proceeding paragraphs wherein the impeding ofthe further detection comprises comparing of the first measure and thesecond proportion, wherein this comparing represents a determination ofwhether an RMS value calculated from approximately ten to fifteenseconds of respiratory flow data exceeds a threshold of approximatelyseventy five percent of an RMS value calculated from approximately fiftyto seventy seconds of respiratory flow data and wherein the secondperiod of time is approximately ten to twenty seconds.

The method of any of the proceeding paragraphs further comprisingmeasuring a flow of breathable gas with a flow sensor.

A hypopnea detection apparatus comprising: a controller having at leastone processor to access data representing a measured flow of breathablegas, the controller being further configured to: determine a firstmeasure from a short-term variance of the data; determine a secondmeasure from a long-term variance of the data; compare the first measurewith first and second proportions of the second measure; and indicate adetection of the hypopnea based on the comparing if the first measurefalls below the first proportion and does not subsequently exceed arange of the first and second proportions during a first time period.

The apparatus of any of the proceeding paragraphs wherein the firstproportion is less than the second proportion and wherein the controlleris further configured to indicate a detection of a hypopnea if the firstmeasure does not exceed the first proportion during the first timeperiod.

The apparatus of any of the proceeding paragraphs wherein the firstproportion is less than the second proportion and wherein the controlleris further configured to indicate a detection of a hypopnea if the firstmeasure exceeds the first proportion but does not exceed the secondproportion during the first time period.

The apparatus of any of the proceeding paragraphs wherein the controlleris further configured to detect a measure of flow limitation from thedata and wherein the indicating the detection of the hypopnea is furtherbased on the measure of flow limitation being indicative of obstruction.

The apparatus of any of the proceeding paragraphs wherein the comparingof the first measure and the first proportion represents a determinationof whether an RMS value calculated from approximately ten to fifteenseconds of respiratory flow data falls below a threshold ofapproximately fifty percent of an RMS value calculated fromapproximately fifty to seventy seconds of respiratory flow data andwherein the first period of time is approximately three to eightseconds.

The apparatus of any of the proceeding paragraphs wherein the comparingof the second measure and the second proportion represents adetermination of whether an RMS value calculated from approximately tento fifteen seconds of respiratory flow data is below a threshold ofapproximately seventy five percent of an RMS value calculated fromapproximately fifty to seventy seconds of respiratory flow data.

The apparatus of any of the proceeding paragraphs wherein the comparingof the first measure and the first proportion represents a determinationof whether an RMS value calculated from approximately ten to fifteenseconds of respiratory flow data falls below a threshold ofapproximately fifty percent of an RMS value calculated fromapproximately fifty to seventy seconds of respiratory flow data andwherein the first period of time is approximately three to eightseconds.

The apparatus of any of the proceeding paragraphs wherein the controlleris further configured to impede a further detection of a hypopnea untilthe first measure exceeds the second proportion during a second periodof time.

The apparatus of any of the proceeding paragraphs wherein the impedingof the further detection comprises comparing of the first measure andthe second proportion, wherein this comparing represents a determinationof whether an RMS value calculated from approximately ten to fifteenseconds of respiratory flow data exceeds a threshold of approximatelyseventy five percent of an RMS value calculated from approximately fiftyto seventy seconds of respiratory flow data and wherein the secondperiod of time is approximately ten to twenty seconds.

The apparatus of any of the proceeding paragraphs further comprising aflow sensor and wherein the controller is further configured todetermine the measured flow of breathable gas with the flow sensor.

The apparatus of any of the proceeding paragraphs further comprising: aflow generator configured to produce a breathable gas for a patient at apressure above atmospheric pressure; wherein the controller is furtherconfigured to control the flow generator to produce the breathable gasaccording to a pressure therapy regime based on the detected hypopnea.

A method for controlling a processor to detect a hypopnea from ameasured flow of breathable gas, the method of the processor comprising:determining a long-term measure of ventilation; determining a short-termmeasure of ventilation; determining a threshold as a proportion of thelong-term measure of ventilation; measuring an area bounded by first andsecond crossings of the short-term measure of ventilation and thethreshold; and detecting the hypopnea with the measured area.

The method of any of the preceding paragraphs wherein the measuringcomprises integrating a difference between the threshold and theshort-term measure of ventilation during a time period from when theshort-term measure falls below the threshold to when the short-termmeasure exceeds the threshold.

The method of any of the preceding paragraphs wherein the measuringcomprises adding a plurality of sample differences during a time periodfrom when the short-term measure falls below the threshold to when theshort-term measure exceeds the threshold, wherein each sample differenceis a difference between a sample of the threshold and a sample of theshort-term measure of ventilation.

The method of any of the preceding paragraphs further comprisingimpeding a further detection of a hypopnea during a refractory periodinitiated at the second crossing.

The method of any of the preceding paragraphs further comprisingtriggering the measuring of the area upon detecting the first crossingby comparing the short-term measure of ventilation and the threshold forinequality.

The method of any of the preceding paragraphs wherein the detecting ofthe hypopnea is contingent upon a time from the first crossing to thesecond crossing exceeding about ten seconds.

The method of any of the preceding paragraphs wherein the short-termmeasure of ventilation comprises an output of low pass filtering half ofan absolute value of a measure of flow of breathable gas with a firsttime constant.

The method of any of the preceding paragraphs wherein the long-termmeasure of ventilation comprises an output of low pass filtering half ofan absolute value of a measure of flow of breathable gas with a secondtime constant, the second time constant being larger than the first timeconstant.

The method of any of the preceding paragraphs wherein the proportioncomprises approximately seventy percent.

The method of any of the preceding paragraphs further comprisingindicating a severity of the hypopnea with the measure of area.

The method of any of the preceding paragraphs wherein the detectingcomprises comparing the measured area with a threshold chosen to beapproximately indicative of a desaturation of blood oxygen of at leastfour percent.

The method of any of the preceding paragraphs further comprisingmeasuring a flow of breathable gas with a flow sensor.

The method of any of the preceding paragraphs further comprisingdetecting a measure of flow limitation from the measured flow signal andwherein the detection of the hypopnea is further based on the measure offlow limitation being indicative of obstruction.

An apparatus to detect a hypopnea from a measured flow of breathablegas, the apparatus comprising: a controller having at least oneprocessor to access data representing a measured flow of breathable gas,the controller being further configured to: determine a long-termmeasure of ventilation from the measured flow; determine a short-termmeasure of ventilation from the measured flow; determine a threshold asa proportion of the long-term measure of ventilation; measure an areabounded by first and second crossings of the short-term measure ofventilation and the threshold; and detect the hypopnea with the measuredarea.

The apparatus of any of the preceding paragraphs wherein the controlleris configured to measure the area by integrating a difference betweenthe threshold and the short-term measure of ventilation during a timeperiod from when the short-term measure falls below the threshold towhen the short-term measure exceeds the threshold.

The apparatus of any of the preceding paragraphs wherein the controlleris configured to measure the area by adding a plurality of sampledifferences during a time period from when the short-term measure fallsbelow the threshold to when the short-term measure exceeds thethreshold, wherein each sample difference is a difference between asample of the threshold and a sample of the short-term measure ofventilation.

The apparatus of any of the preceding paragraphs wherein the controlleris further configured to impede a further detection of a hypopnea duringa refractory period initiated by detection of the second crossing.

The apparatus of any of the preceding paragraphs wherein the controlleris further configured to trigger the measuring of the area upondetecting the first crossing by comparing the short-term measure ofventilation and the threshold for inequality.

The apparatus of any of the preceding paragraphs wherein the detectionof the hypopnea is contingent upon a time from the first crossing to thesecond crossing exceeding about ten seconds.

The apparatus of any of the preceding paragraphs wherein the short-termmeasure of ventilation comprises an output of low pass filtering half ofan absolute value of a measure of flow of breathable gas with a firsttime constant.

The apparatus of any of the preceding paragraphs wherein the long-termmeasure of ventilation comprises an output of low pass filtering half ofan absolute value of a measure of flow of breathable gas with a secondtime constant, the second time constant being larger than the first timeconstant.

The apparatus of any of the preceding paragraphs wherein the proportioncomprises approximately seventy percent.

The apparatus of any of the preceding paragraphs wherein the controlleris further configured to indicate a severity of the hypopnea with themeasure of area.

The apparatus of any of the preceding paragraphs wherein the detectingcomprises comparing the measured area with a threshold chosen to beapproximately indicative of a desaturation of blood oxygen of at leastfour percent.

The apparatus of any of the preceding paragraphs wherein the controlleris further configured to detect a measure of flow limitation from thedata and wherein the detection of the hypopnea is further based on themeasure of flow limitation being indicative of obstruction.

The apparatus of any of the preceding paragraphs further comprising aflow sensor and wherein the controller is further configured todetermine the measured flow of breathable gas with the flow sensor.

The apparatus of any of the preceding paragraphs further comprising: aflow generator configured to produce a breathable gas for a patient at apressure above atmospheric pressure; wherein the controller is furtherconfigured to control the flow generator to produce the breathable gasaccording to a pressure therapy regime based on the detected hypopnea.

A method for controlling a processor to detect a hypopnea from ameasured flow of breathable gas, the method of the processor comprising:determining a long-term measure of ventilation; determining a short-termmeasure of ventilation; determining a threshold as a proportion of thelong-term measure of ventilation; calculating an extent of a hypopnea asa function of the short-term measure of ventilation and the threshold;and indicating a severity of the hypopnea with the measured extent.

The method of any of the preceding paragraphs wherein the indicatingcomprises outputting a value of the measured extent.

The method of any of the preceding paragraphs wherein the calculatedextent is a calculated area bounded by first and second crossings of theshort-term measure of ventilation and the threshold.

The method of any of the preceding paragraphs further comprisingcomparing the calculated area with a threshold chosen to beapproximately indicative of a desaturation of blood oxygen of at leastfour percent.

The method of any of the preceding paragraphs further comprisingmeasuring a flow of breathable gas with a flow sensor.

The method of any of the preceding paragraphs further comprisingdetecting a measure of flow limitation from the measure flow and whereinthe indicating the detection of the hypopnea is further based on themeasure of flow limitation being indicative of obstruction.

An apparatus to detect a hypopnea from a measured flow of breathablegas, the apparatus comprising: a controller having at least oneprocessor to access data representing a measured flow of breathable gas,the controller being further configured to: determine a long-termmeasure of ventilation from the data; determine a short-term measure ofventilation from the data; determine a threshold as a proportion of thelong-term measure of ventilation; calculate an extent of a hypopnea as afunction of the short-term measure of ventilation and the threshold; andindicate a severity of the hypopnea with the calculated extent.

The apparatus of any of the preceding paragraphs wherein the controlleris configured to indicate the severity by outputting a value of thecalculated extent to an output device.

The apparatus of any of the preceding paragraphs wherein the controllercalculates the extent by calculating an area bounded by first and secondcrossings of the short-term measure of ventilation and the threshold.

The apparatus of any of the preceding paragraphs wherein the controlleris further configured to compare the calculated area with a thresholdchosen to be approximately indicative of a desaturation of blood oxygenof at least four percent.

The apparatus of any of the preceding paragraphs further comprising aflow sensor and wherein the controller is further configured todetermine the measured flow of breathable gas with the flow sensor.

The apparatus of any of the preceding paragraphs further comprising: aflow generator configured to produce a breathable gas for a patient at apressure above atmospheric pressure; wherein the controller is furtherconfigured to control the flow generator to produce the breathable gasaccording to a pressure therapy regime based on the detected hypopnea.

The apparatus of any of the preceding paragraphs wherein the controlleris further configured to detect a measure of flow limitation from thedata and wherein the indicating the detection of the hypopnea is furtherbased on the measure of flow limitation being indicative of obstruction.

A method for controlling a processor to classify a hypopnea from ameasured flow of breathable gas, the method of the processor comprising:detecting an hypopnea event from a measured flow of breathable gas;determining a measure indicative of obstruction in the measured flowcoincident with the hypopnea event; and classifying the detectedhypopnea event as obstructive or central based on the determining of themeasure indicative of obstruction.

The method of any of the preceding paragraphs wherein the determiningcomprises detecting partial obstruction and the classifying comprisesscoring an obstructive hypopnea event.

The method of any of the preceding paragraphs further comprisingdetecting an absence of a breath and the classifying comprises scoring acentral hypopnea event.

The method of any of the preceding paragraphs further comprisingdetecting an absence of a breath coincident with a further detectedhypopnea event and refraining from scoring the further detected hypopneaevent based on the detected absence of a breath.

A hypopnea detection apparatus comprising: a controller having at leastone processor to access data representing a measured flow of breathablegas, the controller being further configured to control: a detection ofan hypopnea event from the data representing the measured flow ofbreathable gas; a determination of a measure indicative of obstructioncoincident with the hypopnea event in the data representing the measuredflow; and a classification the detected hypopnea event as obstructive orcentral based on the determining of the measure indicative ofobstruction.

The apparatus of any of the preceding paragraphs wherein thedetermination detects partial obstruction and the classificationcomprises scoring an obstructive hypopnea event.

The apparatus of any of the preceding paragraphs wherein the controlleris further configured to control a detection of an absence of a breathand the classification comprises scoring a central hypopnea event.

The apparatus of any of the preceding paragraphs wherein the controlleris further configured to detect an absence of a breath coincident with afurther detected hypopnea event and to refrain from scoring the furtherdetected hypopnea event based on the detected absence of a breath.

The apparatus of any of the preceding paragraphs further comprising: aflow generator configured to produce a breathable gas for a patient at apressure above atmospheric pressure; and a flow sensor, wherein thecontroller is further configured to measure the flow of breathable gaswith the flow sensor and to control the flow generator to produce thebreathable gas according to a pressure therapy regime based on thedetected hypopnea.

The invention claimed is:
 1. A hypopnea detection apparatus comprising:a controller having at least one processor to access data representing ameasured flow of breathable gas, the controller being further configuredto: determine a first measure from the flow data, the measurerepresenting a short-term ventilation; determine a second measure fromthe flow data, the measure representing a long-term ventilation; comparethe first measure with first and second proportions of the secondmeasure; and indicate a detection of the hypopnea based on the comparingif the first measure is below the first proportion at a start and an endof a first time period, while remaining below the second proportionthroughout the first time period.
 2. The apparatus of claim 1 whereinthe first proportion is less than the second proportion and wherein thecontroller is further configured to indicate a detection of a hypopneaif the first measure does not exceed the first proportion during thefirst time period.
 3. The apparatus of claim 1 wherein the firstproportion is less than the second proportion and wherein the controlleris further configured to indicate a detection of a hypopnea if the firstmeasure exceeds the first proportion but does not exceed the secondproportion during the first time period.
 4. The apparatus of claim 1wherein the controller is further configured to detect a measure of flowlimitation from the data and wherein the indicating the detection of thehypopnea is further based on the measure of flow limitation beingindicative of obstruction.
 5. The apparatus of claim 1 wherein thecomparing of the first measure and the first proportion represents adetermination of whether an RMS value calculated from approximately tento fifteen seconds of respiratory flow data falls below a threshold ofapproximately fifty percent of an RMS value calculated fromapproximately fifty to seventy seconds of respiratory flow data andwherein the first period of time is approximately three to eightseconds.
 6. The apparatus of claim 1 wherein the comparing of the firstmeasure and the second proportion represents a determination of whetheran RMS value calculated from approximately ten to fifteen seconds ofrespiratory flow data is below a threshold of approximately seventy fivepercent of an RMS value calculated from approximately fifty to seventyseconds of respiratory flow data.
 7. The apparatus of claim 6 whereinthe comparing of the first measure and the first proportion represents adetermination of whether an RMS value calculated from approximately tento fifteen seconds of respiratory flow data falls below a threshold ofapproximately fifty percent of an RMS value calculated fromapproximately fifty to seventy seconds of respiratory flow data andwherein the first period of time is approximately three to eightseconds.
 8. The apparatus of claim 1 wherein the controller is furtherconfigured to impede a further detection of a hypopnea until the firstmeasure exceeds the second proportion during a second period of time. 9.The apparatus of claim 8 wherein the impeding of the further detectioncomprises comparing of the first measure and the second proportion,wherein this comparing represents a determination of whether an RMSvalue calculated from approximately ten to fifteen seconds ofrespiratory flow data exceeds a threshold of approximately seventy fivepercent of an RMS value calculated from approximately fifty to seventyseconds of respiratory flow data and wherein the second period of timeis approximately ten to twenty seconds.
 10. The apparatus of claim 1further comprising a flow sensor and wherein the controller is furtherconfigured to determine the measured flow of breathable gas with theflow sensor.
 11. The apparatus of claim 10 further comprising: a flowgenerator configured to produce a breathable gas for a patient at apressure above atmospheric pressure; wherein the controller is furtherconfigured to control the flow generator to produce the breathable gasaccording to a pressure therapy regime based on the detected hypopnea.12. The apparatus of claim 1 wherein the first measure is a short-termvariance and the second measure is a long-term variance.
 13. Thehypopnea detection apparatus of claim 1 wherein the controller isfurther configured to indicate a detection of the hypopnea based on thecomparing if the first measure falls below the first proportion andenters but does not subsequently exceed a range of the first and secondproportions, the indication being during the first time period when thefirst measure subsequently falls below the first and second proportions.14. A hypopnea detection method comprising: with a processor to accessdata representing a measured flow of breathable gas: determining a firstmeasure from the flow data, the measure representing a short-termventilation; determining a second measure from the flow data, themeasure representing a long-term ventilation; comparing the firstmeasure with first and second proportions of the second measure; andindicating a detection of the hypopnea based on the comparing if thefirst measure is below the first proportion at a start and an end of afirst time period, while remaining below the second proportionthroughout the first time period.
 15. The method of claim 14 wherein thefirst proportion is less than the second proportion and wherein theprocessor indicates a detection of a hypopnea if the first measure doesnot exceed the first proportion during the first time period.
 16. Themethod of claim 14 wherein the first proportion is less than the secondproportion and wherein the processor indicates a detection of a hypopneaif the first measure exceeds the first proportion but does not exceedthe second proportion during the first time period.
 17. The method ofclaim 14 wherein the processor detects a measure of flow limitation fromthe data and wherein the indicating the detection of the hypopnea isfurther based on the measure of flow limitation being indicative ofobstruction.
 18. The method of claim 14 wherein the comparing of thefirst measure and the first proportion represents a determination ofwhether an RMS value calculated from approximately ten to fifteenseconds of respiratory flow data falls below a threshold ofapproximately fifty percent of an RMS value calculated fromapproximately fifty to seventy seconds of respiratory flow data andwherein the first period of time is approximately three to eightseconds.
 19. The method of claim 14 wherein the comparing of the firstmeasure and the second proportion represents a determination of whetheran RMS value calculated from approximately ten to fifteen seconds ofrespiratory flow data is below a threshold of approximately seventy fivepercent of an RMS value calculated from approximately fifty to seventyseconds of respiratory flow data.
 20. The method of claim 19 wherein thecomparing of the first measure and the first proportion represents adetermination of whether an RMS value calculated from approximately tento fifteen seconds of respiratory flow data falls below a threshold ofapproximately fifty percent of an RMS value calculated fromapproximately fifty to seventy seconds of respiratory flow data andwherein the first period of time is approximately three to eightseconds.
 21. The method of claim 14 further comprising with theprocessor impeding a further detection of a hypopnea until the firstmeasure exceeds the second proportion during a second period of time.22. The method of claim 21 wherein the impeding of the further detectioncomprises comparing of the first measure and the second proportion,wherein this comparing represents a determination of whether an RMSvalue calculated from approximately ten to fifteen seconds ofrespiratory flow data exceeds a threshold of approximately seventy fivepercent of an RMS value calculated from approximately fifty to seventyseconds of respiratory flow data and wherein the second period of timeis approximately ten to twenty seconds.
 23. The method of claim 14further comprising measuring with a sensor a breathable gas to determinethe measured flow.
 24. The method of claim 23 further comprisingcontrolling with the processor a flow generator configured to produce abreathable gas for a patient at a pressure above atmospheric pressure,the controlling comprising setting the flow generator to produce thebreathable gas according to a pressure therapy regime based on thedetected hypopnea.
 25. The method of claim 14 wherein the first measureis a short-term variance and the second measure is a long-term variance.26. The hypopnea detection method of claim 14 further comprising withthe processor indicating a detection of the hypopnea based on thecomparing if the first measure falls below the first proportion andenters but does not subsequently exceed a range of the first and secondproportions, the indication being during the first time period when thefirst measure subsequently falls below the first and second proportions.